Rocks ready to make planets seen for the first time
Lumps of rock in the process of forming planets have been detected for the very first time
An artist’s impression of the belt of ‘pebbles’ in orbit around the star DG Tauri. Image Credit: ESO/L. Calçada/M. Kornmesser, ALMA (ESO/NAOJ/NRAO)/L. Calçada (ESO)
A ring of rocks suspected to be an important link in the making of planets has been detected for the very first time.
It’s long been thought that planets are constructed from dust and gas in orbit around a baby star. The dust particles stick together over time, snowballing into even bigger clumps of rock. When enough mass is gained, gravity begins to become significant and, millions of years later, these boulders begin to smash into each other, often ensuring the beginnings of planets and moons.
Astronomers have had no difficulty in locating discs of gas and dust as well as nearly 2000 planets that have almost completed their formation. However, the stage in between these extremes has been a lot harder to find – until now. Using e-MERLIN – a sensitive array of radio telescopes, which stretches across England and has a central Hub at Jodrell Bank in Cheshire – a team of astronomers at the universities of Manchester and St. Andrews noticed DG Tauri, a youthful star just 2.5 million years old and around 450 light years away from us.
“We knew DG Tauri had a jet of hot gas flowing off its poles – a beacon for stars still in the process of forming – so we had an idea of what to look for,” says team member Anita Richards from the University of Manchester.
The 76 metre-diameter Lovell Telescope at Jodrell Bank, which is the heart of the e-MERLIN array. Image Credit: Mike Peel
Richards’ colleague Jane Greaves of the University of St. Andrews adds: “The extraordinarily fine detail we can see with the e-MERLIN telescopes was the key to this discovery. We could zoom into a region as small as the orbit of Jupiter would be in the Solar System,” says Greaves, who leads an international team known as PEBBLeS, an acronym for the Planet Earth Building Blocks Legacy e-MERLIN Survey. “We found a belt of pebbles strung along a very similar orbit – just where they are needed if a planet is to grow in the next few million years. Although we thought this was how planets must get started, it’s very exciting to actually see the process in action!”
Greaves and her team intend to image as many rocky belts in orbit around young stars as possible. This will allow them to hunt for the clues that will hopefully hint towards how often planets form around stars that evolve in the future to be like our very own Sun. Eventually – and with the advent of upgrades to e-MERLIN’s capabilities over the next few years – the aim is to zoom in on a young system and witness an extrasolar Earth being born.
“Long wavelength data, such these fantastic e-MERLIN results, will be essential in constraining the next generation of computer models of discs around young star,” says team member John Lee also based at the University of St. Andrews. “Having an accurate idea of the location and amount of the centimetre-sized material in the disc will bring us closer to a consistent picture of how planets may eventually form.”
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